Quill knobs for Dakotaraptor's feather attachment match those of modern birds. |
Robert DePalma

The fossils indicated the presence of "quill knobs" (see photo above) pointing to where feathers would have been attached to the creature's forearms. The knobs are "our first clear evidence for feather quills on a large dromaeosaurid forearm," DePalma and his team wrote in a paper detailing their findings.

In addition to the wonder of the giant raptor's size in its own right, the find helps scientists sketch a clearer picture of the pecking order at the time.

"This new predatory dinosaur also fills the body size gap between smaller theropods and large tyrannosaurs that lived at this time," said University of Kansas paleontologist and study co-author David Burnham.

Paleontologists have just assembled the most comprehensive family tree of meat-eating dinosaurs. Published in the journal Current Biology, the family tree reveals how diverse carnivorous dinosaurs were and how birds eventually evolved from them.
Tyrannosaurs, including

Tyrannosaurus rex

, are one key group on the meat-loving dino family tree. Lead author Steve Brusatte of the University of Edinburgh's School of GeoSciences told Discovery News, "The most iconic dinosaurs of all, tyrannosaurs were more than just the 13-meter-long (nearly 43 feet long), 5-ton monster predator

T. rex

."
"Tyrannosaurs were an ancient group that originated more than 100 million years before

T. rex

, and for almost all of their evolutionary history they were small carnivores not much bigger than a human in size."

"Some of the rarest theropods (two-legged carnivorous dinos) of all, compsognathids are represented by about half a dozen species," Brusatte said. "They were small, sleek meat-eaters which ate small prey like lizards."
One of the more recent finds, Juravenator from Germany, is known from a nearly complete fossil.

Ornithomimosaurs were theropods called "ostrich mimic" dinosaurs -- for a reason.
"Like living ostriches, they could run fast on their long legs and used their sharp, toothless beaks to eat a varied diet of small prey, plants, and perhaps even small shrimps in the water just like living flamingos," Brusatte explained.
"A recent find in Canada showed that not only were ornithomimosaurs feathered, but they also had complex feathers on their arms that would have formed something of a wing, although they couldn't fly."

Brusatte describes therizinosaurs as "perhaps the weirdest theropods of all."
"These were big, bulky, cumbersome dinosaurs that ate plants. They had fat barrel-shaped chests, stocky legs, and big claws on their arms," Brusatte said.
For many years paleontologists argued about which group this dinosaur belonged to, only recently settling on theropods. This means they were fairly closely related to birds, despite their weird anatomy.

Alvarezsaurs were among the smallest dinosaurs of all, measuring just a few feet long and weighing less than 5 kilograms (10 pounds).
"Some of them had only a single functional finger on their hand, which they probably used to prod deep into the nests of bugs, which were one of their main food sources," Brusatte said.

"Troodontids were probably the smartest dinosaurs of all, as they had the largest brains relative to their body size of any dinosaur group," Brusatte said. "Most troodontids were small, fast-running dinosaurs that probably ate both meat and plants."
Among the most recently discovered of this group are the small, feathered Anchiornis and Xiaotingia, which lived in China about 160 million years ago.
"They look eerily similar to birds, so much so that some researchers think they could be primitive birds rather than troodontids with wings and feathers," Brusatte said.

Dromaeosaurids were "raptor dinosaurs" that include Velociraptor from "Jurassic Park" fame.
These dinosaurs were pack hunters who wielded a sharp, hyper-extendable "killer claw" on their second toe.
"One of the most recently discovered dromaeosaurids is Balaur, a poodle-sized terror from Romania which had not one, but two 'killer claws' on each foot."

"The oldest birds, like Archaeopteryx that lived 150 million years ago in Germany, are very hard to distinguish from their closest dinosaurian relatives," Brusatte said. "Unlike living birds, they had teeth, sharp claws on their wings, and long tails."
"Over the past two decades," he continued, "over 50 new species of Mesozoic birds have been discovered in northeastern China, in the same rock units as the famous 'feathered dinosaurs.' So many birds are preserved here because entire ecosystems were buried by volcanic eruptions, turning animals to stone like a dinosaur version of Pompeii."

"The 10,000 species of birds that live today -- from hummingbirds to ostriches -- are modern dinosaurs," Brusatte said. "They are dinosaurs in the same way that humans are mammals. The classic body plan of living birds -- feathers, wings, wishbones, air sacs extending into hollow bones -- did not evolve suddenly but was gradually assembled over tens of millions of years of evolution. But, when this body plan finally came together completely, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate."
"They underwent a burst of evolution early in their history, which eventually led to the 10,000 species alive today -- more than twice the number of mammals."